The reason you cannot find your name under German origins is because it is not a German name.
Coming from the Alsace, there is a mixture of German and French family names, since this area belonged at one time to the Holy Roman Empire, then to Germany, then to France, and then to Germany, and now again to France.
Your name is almost surely from the French word "cloueur", which means someone who makes or sells nails, or is a nailer.
The word "clou" is the French word for "a nail"
In modern French, for example, "un cloueur pneumatique" is a pneumatic (automatic) nailer.
Former teacher of German and French